Re: Gst::PlayBin2 signal_get_audio_tags trouble

[José Alburquerque <jaalburquerque cox net>]

On Sun, 2009-12-13 at 11:27 +0100, kitone wrote: 
> Hi,
> I've some trouble to using the Gst::PlayBin2 element, specially the
> signals signal_get_*_tags.
> 
> With gstreamer (C) we can used g_signal_emit_by_name to received the
> tags. ex:
> 
>  for (i = 0; i < n_audio; i++) {
>    g_signal_emit_by_name (pipeline, "get-audio-tags", i, &tags);
>    ...
> 
> Now, how can I do used the Gst::PlayBin2::signal_get_audio_tags to
> receive the tags list ? In this case, connect to my own callback is not
> what I want to do and I don't thing is what we need to do, I'm wrong ?

No, you're not wrong (I think).  What's wrong was my understanding of
these signals.  Apparently, these are "action" signals (which I was not
fully aware of).  From the docs[1], they can be thought of as object
methods that can be called generically (sort of like how a regular
method might be used).

[1]
http://library.gnome.org/devel/gobject/2.22/gobject-Signals.html#GSignalFlags

One way to get similar functionality in C++ is to include an equivalent
method definition in the plug-in source to emit the signal with the
right parameters and generate the correct return.

Another way (more general, but would affect all *mm module signals)
would be to make it possible for the Glib::SignalProxy<> classes to emit
their corresponding signals.

The first way (modifying the plug-in sources) is easily achievable by
modifying the plug-in generation tool in gstreamermm.  The second also
seems possible but only from having quickly skimmed the
Glib::SignalProxy<> source code.

To get this right I know I could work on the first way fairly quickly.
I can also submit a patch for the second, but that would require
approval from the glibmm maintainers.

For now, I guess that using the Gst::PlayBin2's gobj() with the C API
and the Gst::TagList's specific Glib::wrap() method to wrap the
resulting GstTagList would be the way to do things until this is
resolved in an upcoming release.

-- 
José